Electrical Safety & PPE before an Arc Flash Analysis

(This is the first of a series of articles on this subject. Look next week for Part II: Gaps & Problems with the NFPA 70E 130.7 Chart.)

The primary outcome of an Arc Flash Analysis is to identify arc flash risk hazard levels for workers, warn the workers about the hazards by placing labels on the equipment. From that, the employer needs to provide the proper PPE to protect the workers from the hazards and train them on how to use the PPE.

The problem many companies face is that completing an Arc Flash Analysis can be both an expensive and time consuming proposition. For some companies, just getting the money in the budget and getting it approved can take a year or more. If you have a lot of facilities or a large complex, the arc flash analysis itself can also be a time consuming process taking months or even years to do all buildings. So in the time between planning an arc flash analysis and one actually being done, what do you do to protect workers and start down the road towards compliance?

About Using the NFPA 70E 130.7 Chart

Using the NFPA 70E 130.7 Chart as an alternative to an arc flash analysis simply isn’t possible or a viable alternative for most companies. It’s very rare that a company has the right information to actually use the charts as they were designed and getting the information can be almost as expensive as an arc flash analysis itself. Further, the 130.7 Chart has some gaps in it that will not allow you to always use the chart, will require you to do an arc flash analysis or do not provide enough information to provide a proper warning.

Requirements to Use the NFPA 70E 130.7 Chart

Properly using the NFPA 70E 130.7 Chart requires that:

1. The short circuit current available and fault clearing time is known for the electrical equipment.
2. The short circuit current and fault clearing times of the equipment fall within the parameters of the
chart footnotes.
3. That the task being performed falls within the parameters of the chart.

If a) the task is not listed or b) the short circuit current and fault clearing times are not known or c) if the short circuit current and fault clearing times are greater than the assumed numbers in the footnotes of the chart, one can not use the chart and an arc flash analysis shall be required in accordance with 130.3 of NFPA 70E.

It is very rare when a company knows their short circuit or fault clearing times since it requires an engineering analysis from the point of service from the utility to the piece of equipment in question. This analysis determines the fault current by starting with the utility provided fault current at the point of entry, then determining the elements that attenuate this current downstream to the point in question. The clearing time is not a fixed number for a given protective device, but rather varies significantly with changes in the fault current and adjustments on many breakers.